Iron and zinc are two micronutrients that have been implicated as major causes of maternal and, especially, infant morbidity in the developing world. Dietary intakes of minerals are not necessarily low, but bioavailability of these minerals is poor. Efforts to overcome the inadequate quantities of bioavailable mineral by supplementation or fortification are complicated by uncertainties about the bioavailability of the added mineral, with the concomitant risk of continuing deficiency on the one hand (aggravated by poor compliance) and, possibly, excess on the other. The large quantities of phytic acid present in vegetablebased diets, typical of developing countries, especially in unrefined cereal grains and legumes, are widely considered to be the major factor (together with low heme iron) responsible for poor mineral bioavailability and status. This hypothesis will be tested in the rural Western Highlands of Guatemala, where maize (treated with lime) is the principal dietary staple, by long-term dietary phytate reduction utilizing low phytate (65% reduction) maize. The duration of this intervention in 500 women (parity 1-2)-and their infants-will be from at least 6 months pre-conception to one year post-partum. Women will be randomized to a low phytate group (gr 1); low phytate plus a 15mg prenatal (12-40 weeks gestation) and 2.5 mg older infant 612 months) Zn supplement (gr 2) or to a wild type control group (gr 3). All groups will receive 30mg Fe daily from 12-40 weeks gestation and group 2 infants will receive 7.5 mg Fe /day from 6-12 months. The efficacy of these interventions will be assessed by longitudinal quantitative measurements of: variables of zinc homeostasis; biomarkers of iron and zinc status; selected maternal indices of morbidity and obstetric outcome; indices of fetal and infant growth and development, including neurobehavioral; and selected indices of infant infectious disease morbidity and immune status. If beneficial, this intervention is potentially simple to sustain and disseminate. In Chile, the hypothesis that nutritional intra-uterine growth retardation (a major cause of morbidity in developing countries) is associated with low neonatal zinc stores will be examined with stable isotope techniques.